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Abstract:

A quartz transducer having four or more crystal-controlled oscillators
intended for measurement of applied pressure and temperature. All four
oscillators are controlled by crystal quartz resonators operating in the
thickness-shear mode. Two crystals measure the pressure and temperature
respectively. A third crystal is a reference, and the fourth crystal may
be another reference crystal or a second temperature crystal. The output
of the latter is either phase leading or phase lagging the thermal
response of the main temperature sensor.

Claims:

1. A transducer assembly, comprising: first, second, third, and fourth
crystal controlled oscillators; first, second, third, and fourth
thickness shear mode crystal quartz resonators, wherein the first,
second, third, and fourth oscillators are respectively controlled by the
first, second, third, and fourth, crystal quartz resonators; wherein the
first crystal quartz resonator and the second crystal quartz resonator
respectively comprise a pressure resonator and a reference resonator that
are configured together as a pressure sensor providing a frequency
output; wherein the third crystal quartz resonator comprises a
temperature resonator that is configured as a temperature sensor
providing a frequency output; and wherein the fourth crystal quartz
resonator is comprises a temperature sensor.

2. A transducer assembly as defined in claim 1, wherein the pressure
resonator and the reference resonator are individually mounted or are
mounted together in a holder.

3. A transducer assembly as defined in claim 2, in which the holder has
an inert hydraulic fluid fill which houses the pressure resonator and is
exposed to applied pressure through a process isolating bellows.

4. A transducer assembly as defined in claim 1, wherein the pressure
resonator and the reference resonator are mounted in the same holder to
facilitate an improvement of the thermal response characteristics of the
transducer assembly.

5. A transducer assembly as defined in claim 1, wherein the temperature
resonator and the reference resonator can be individually mounted or
mounted in the same housing or holder.

6. A transducer assembly as defined in claim 5, wherein the reference
resonator and the temperature resonator are mounted in the same holder to
facilitate an improvement of the thermal response characteristics of the
transducer assembly.

7. A transducer assembly as defined in claim 1, wherein the fourth
crystal quartz resonator comprises a second temperature resonator and is
part of the same holder as the reference resonator and the temperature
resonator or is part of a different holder.

8. A transducer assembly as defined in claim 7, wherein the temperature
resonator and the second temperature resonator have the same
temperature-to-frequency characteristics.

9. A transducer assembly as defined in claim 7, wherein a frequency
output of the fourth oscillator is mixed with a frequency output of the
third oscillator to derive a dynamic thermal output.

10. A transducer assembly as defined in claim 7, wherein the temperature
resonator and the second temperature resonator are individual units and
are mounted in different holders or are mounted in a common or the same
holder and provide first and second characteristic thermal time
constants, respectively.

11. A transducer assembly as defined in claim 10, wherein the first and
second thermal time constants are different.

12. A transducer assembly as defined in claim 10, wherein the mixing
combining the frequency outputs of the fourth oscillator and the third
oscillator produces an output signal, having a response that is dynamic
and is related to the temperature difference between the temperature
resonator and the second temperature resonator.

13. A transducer assembly as defined in claim 12, wherein the response is
characterized by the temperature change, the thermal time constants, and
the physical properties of the resonator temperature resonator and the
second temperature resonator.

14. A transducer assembly as defined in claim 12, wherein the response is
related to the physical properties of a transducer housing and the
environment, including the physical properties of the latter.

15. A transducer assembly as defined in claims 12, wherein the difference
in temperature is used together with a temperature sensor output as
inputs to dynamic feed-forward correction systems.

16. A transducer assembly as defined in claim 15, wherein the dynamic
feed-forward correction system is used to provide dynamic correction of
the transducer pressure determination.

17. A transducer assembly as defined in claim 15, wherein the dynamic
feed-forward correction system is used to provide dynamic correction of
the transducer temperature determination.

18. A transducer assembly as defined in claim 15, wherein the dynamic
feed-forward correction system will improve the thermal response of the
transducer pressure determination since the dynamics of the output signal
is a true and real measure of the transducer thermal stability and can be
effectively used to predict when and how much corrective action is needed
to eliminate gross pressure offsets during gradients.

19. A transducer assembly as defined in claim 15, wherein the dynamic
feed-forward correction system will improve the thermal response of the
transducer temperature determination since the dynamics of the output
signal is a true and real measure of the transducer thermal stability and
can be effectively used to predict when and how much corrective action is
needed to eliminate gross temperature offsets during gradients.

20. A transducer assembly as defined in claims 15, wherein the dynamic
feed-forward correction system applies a method derived to suppress the
offsets induced by implementing a thermal diffusion model inverting the
thermal response of the respective transducer sensor, and in which the
diffusion model, which is a function of the temperature level and the
gradient, improves the phase response of the measurement and speeds up
the transducer performance to monitor the correct pressure and
temperature.

21. A transducer assembly as defined in claim 1, wherein the fourth
crystal quartz resonator comprises a second reference resonator, the
second reference resonator and the temperature resonator being configured
together as a temperature sensor providing frequency output.

22. A transducer assembly as defined in claim 21, wherein the pressure
resonator and the reference resonator are individually mounted or are
mounted in the same holder.

23. A transducer assembly as defined in claim 22, wherein the holder has
an inert hydraulic fluid filling the housing around the pressure
resonator, and is exposed to applied pressure through a process isolating
bellows.

24. A transducer assembly as defined in claims 21, wherein the pressure
resonator and the reference resonator are mounted in the same holder to
facilitate an improvement of the thermal response characteristics of the
transducer assembly.

25. A transducer assembly as defined in claim 21, wherein the temperature
resonator and the second reference resonator can be individual units
individually mounted or mounted in the same holder.

26. A transducer assembly as defined in claim 25, wherein the temperature
resonator and the second reference resonator comprise a temperature
sensor and are mounted in the same holder as the pressure resonator and
the reference resonator.

27. A transducer assembly as defined in claim 25, wherein the temperature
resonator and the second reference resonator are mounted in the holder to
facilitate an improvement of the thermal response characteristics of the
transducer assembly.

28. A transducer assembly as defined in claim 25, wherein the reference
resonator and the second reference resonator have the same
temperature-to-frequency characteristics.

29. A transducer assembly as defined in claim 28, wherein a frequency
output of the second oscillator is mixed with a frequency output of the
fourth oscillator to derive a dynamic thermal output.

30. A transducer assembly as defined in claim 21, wherein each of the
reference resonator and the second reference resonator is an individual
unit and is mounted in a different holder, and provides its own
characteristic thermal time constant.

31. A transducer assembly as defined in claim 21, wherein each of the
reference resonator and the second reference resonator is an individual
unit and is mounted in the same holder, and provides its own
characteristic thermal time constant.

32. A transducer assembly as defined in claim 31, wherein the thermal
time constants are different.

33. A transducer assembly as defined in claim 21, wherein the mixing
combining the frequency outputs of the second oscillator and the fourth
oscillator produces an output signal having a response that is dynamic
and is related to the temperature difference between the reference
resonator and the second reference resonator.

34. A transducer assembly as defined in claim 33, wherein the response is
characterized by the temperature change, the thermal time constants, and
the physical properties of the reference resonator and the second
reference resonator.

35. A transducer assembly as defined in claim 33, wherein the response is
related to the physical properties of a transducer housing, and the
environment, including the physical properties of the latter.

36. A transducer assembly as defined claim 33, wherein the difference in
temperature is used together with a temperature sensor output as inputs
to dynamic feed-forward correction systems.

37. A transducer assembly as defined in claim 36, wherein the dynamic
feed-forward correction system is used to provide dynamic correction of
the transducer pressure determination.

38. A transducer assembly as defined in claim 36, wherein the dynamic
feed-forward correction system is used to provide dynamic correction of
the transducer temperature determination.

39. A transducer assembly as defined in claim 36, wherein the dynamic
feed-forward correction system will improve the thermal response of the
transducer pressure determination since the dynamics of the output signal
is a true and real measure of the transducer thermal stability and can be
effectively used to predict when and how much corrective action is needed
to avoid gross pressure offsets during gradients.

40. A transducer assembly as defined claim 36, wherein the dynamic
feed-forward correction system will improve the thermal response of the
transducer temperature determination since the dynamics of the output
signal is a true and real measure of the transducer thermal stability and
can be effectively used to predict when and how much corrective action is
needed to avoid gross temperature offsets during gradients.

41. A transducer assembly as defined in claim 36, wherein the dynamic
feed-forward correction system is a method derived to suppress the
offsets induced by implementing a thermal diffusion model inverting the
thermal response of the respective transducer sensor, and in which the
diffusion model, which is a function of the temperature level and the
gradient, is added to improve the phase response of the measurement and
speed up the transducer performance to monitor correct pressure and
temperature.

42. A transducer assembly as defined in claim 30, wherein the thermal
time constants are different.

Description:

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates generally to a pressure measuring
device and more particularly to a quartz crystal pressure and temperature
transducer assembly having improved error correction when subjected to
pressure and temperature gradients.

[0002] In nearly all phases of oil and gas exploration and production, it
is essential to have accurate knowledge of both pressure and temperature
at a given or specific location in a reservoir or borehole. For example,
during a production phase, reservoir management engineers currently take
advantage of monitored pressure and temperature in a well and use it for
their indicative and model relationship to map the reservoir and
understand its complexity in order to optimize performance as well as
their assets. Instruments used for this kind of surveying or a
permanently monitoring application generally include a high accuracy
pressure sensor device.

[0003] In prior art systems, quartz pressure and/or temperature
transducers consist of precision quartz resonators and are known to be
very accurate for pressure and temperature determinations. However, their
manufacture and method of thermally compensating is based on stable and
static wellbore conditions where the temperature is uniform throughout
the transducer.

[0004] For example, U.S. Pat. No. 5,231,880, to Ward et al., discloses a
pressure transducer assembly suitable for downhole use and is based upon
crystal quartz resonators and associated electronics to drive and process
the signals. U.S. Pat. No. 5,471,882, to Wiggins, is an improvement on
the pressure transducer level in that the inherent quartz pressure and
temperature resonators have been given a matched thermal response to
temperature changes. However, the aforementioned transducers only provide
static temperature compensation, and are a good representation of prior
art quartz pressure transducers used for borehole applications. The Ward
et al. Patent and the Wiggins Patent provide no form of dynamic
temperature compensation of their pressure and temperature determination
since they provide no means of management for the heat-balance within the
transducers. This limits their effectiveness since they do not predict
the correct pressure and temperature of the environment to which they are
exposed if the conditions are unstable and subject to change, and they
can therefore produce gross offset in the pressure and temperature
determination.

[0005] Typically, an oilwell will have a relatively warm fluid production
from reservoir to surface. As the production flow rises to the surface,
energy will be lost by means of heat transfer in the well. Moreover,
since the production media in the tubing is the warmer medium, a radial
heat flow will appear through the wellbore conduits and out to the
surrounding formation. In turn, the colder the formation gets the more
heat is lost. In a permanent pressure monitor application, the placement
of the quartz pressure transducer is typically somewhere at the outer
boundaries of the wellbore conduit. As heat is lost to the surroundings,
the loss creates cylindrical isothermal temperature surfaces as heat
progress outwards through the wellbore conduits to the formation. In
turn, this makes the location of the transducer significant and dependent
upon a temperature gradient, and the ongoing monitoring application would
require the involvement of dynamic compensation techniques in order to
provide accurate and reliable pressure and temperature determinations.

[0006] Generally, the thermal heat balance of a Quartz Pressure Transducer
in a borehole or oil/gas well will be affected by one or more of the
following parameters: flow rate changes, fluid or gas composition changes
within the production or injection tubing, fluid or gas composition
changes in the annular volumes of the wellbore, direct pressure changes
in the reservoir or induced at the surface, or any combination of the
above. Furthermore, pressure changes in the well will cause temperature
change within the transducer due to adiabatic effects within the
transducer oil-fill as well as the quartz resonator pressure sensor
itself. Moreover, the main concern is the fidelity or faithfulness of the
transducer response as in use it exhibits a continuous rate of change in
temperature induced by the well production and load as well as the
physical properties of the environment. In real well pressure/temperature
monitoring applications, the prior art quartz transducers such as given
in the Ward et al. Patent, the Wiggins Patent, U.S. Pat. No. 4,802,370,
to Eernisse et al., U.S. Pat. No. 3,561,832, to Karrer et al., and U.S.
Pat. No. 3,355,949, to Elwood et al., provide static temperature
compensation only, and they do not compensate for all the variations
which results from the implications considered above. To be more
effective, the application requires a Quartz Pressure and Temperature
Transducer to be dynamic and be adaptable to the changes.

[0007] To provide accurate measurements using crystal quartz sensor
technology in temperature gradient environments, some knowledge and
measurement of the thermal stability of the system and the quartz
transducer is required. Thermal response belongs, fundamentally, in the
realm of transient heat transfer. The rate of response of the quartz
resonator pressure and temperature sensors clearly depends on the
physical properties of the transducer embodiment, the physical properties
of its environment as well as the dynamical properties of its
environment. Amplifying on this, and the fact that physical properties
normally change with temperature, it follows that the response time of
the transducer will vary with the temperature level. Therefore, the
present invention confines attention to make certain necessary
modifications to the traditional transducer design as well as the concept
of how to temperature compensate its outputs. This is achieved by
implementing a dynamic feed-forward compensation technique that is
directly driven by the temperature level and the rate of change in
temperature that the transducer exhibits.

[0008] To manage this task a mathematical thermal model describing the
temperature behavior of the transducer quartz pressure and temperature
resonators is derived. The model is based on a theorem of heat and
energy-balance which defines that heat will not be lost, but can be
moved, accumulated, and/or energy transferred only, and is used for
dynamic compensation means. Further, the transducer is provided with
sensors to measure the temperature level as well as the temperature
gradient. In turn, the temperature level and rate sensor outputs are
inputs to the thermal models and provide means of dynamic feed-forward
correction to the output of the quartz resonator temperature and pressure
sensors. Furthermore, due to the feed-forward technique, it makes the
inherent transducer embodiment become a fast and accurate temperature
compensated pressure and temperature transducer, and not just a
temperature compensated pressure transducer as in the prior art systems.

[0009] It is therefore desirable to predict how much corrective action a
change in temperature will require to correct output data. This has been
greatly improved by the thermal management and signal processing of the
transducer embodiments of this invention. The Quartz Pressure and
Temperature Transducer Assemblies have a split thermal configuration that
includes two individual quartz resonator temperature sensors. This is a
unique feature in that a mixing of the two temperature sensors is a
direct measure of the temperature gradient or heat balance of the
transducer sensors. In turn, the output is dynamic, and controls how much
and when corrective action is required by the feed-forward correction
system in order to minimize the offsets of the transducer pressure and
temperature determinations.

SUMMARY OF THE INVENTION

[0010] The present invention relates in general to a pressure and
temperature measuring device and more particularly to a Quartz Pressure
and Temperature Transducer Assembly with Dynamic Correction intended for
use in non-static environments. To measure pressure and temperature, the
transducer provides a crystal quartz sensor set consisting of one
pressure, two temperature, and one reference resonator. All four crystals
vibrate in the thickness sheer mode and have their own oscillator that
provides a frequency output. The quartz resonator pressure sensor is
sensing the pressure of the media to which the transducer is exposed, and
the output is both pressure and temperature sensitive.

[0011] The two quartz resonator temperature sensors are temperature
sensitive only and have the same temperature versus frequency
characteristics. The function of the first quartz resonator temperature
sensor is two-fold. The first function is to measure the temperature to
which the transducer is exposed, and the second function is to compensate
or correct the static temperature level effects of the quartz resonator
pressure sensor. The function of the second quartz resonator temperature
sensor is to provide means of dynamic correction of the transducer
pressure and temperature determination. More particularly, the output of
the second temperature resonator is mixed with the first, providing a
means of "differential temperature" measurement. The product of the two
is a dynamic measure, directly representing the transducer response to
temperature, and utilizes the usage and the fact that the second
resonator temperature sensor is configured to have a faster response to
temperature change than the first. Amplifying on this, it follows that
the differential temperature measurement derived is a footprint of the
sensor response since it possesses a dynamic output that varies with the
mass velocity of its environment. By dynamic means, this is an ideal
input to use in a feed-forward correction system to provide a fast and
accurate pressure and temperature measurements under non-static
conditions.

[0012] Finally, the quartz resonator reference is used to process the
signals of the pressure and temperature resonators and is typically made
in a Sensitivity Cut ("SC") type cut, which possess very little
temperature sensitivity. The "SC" cut is a doubly rotated crystal quartz
cut which results in the property that the resonator frequency varies
little with wide variations in temperature. The quartz resonator
reference is the "timebase" of the transducer and is used internally as
time and signal reference to mix and to process the frequency signals
from the pressure and temperature sensor oscillators.

[0013] More particularly, the present invention provides a thermal
management consisting of two temperature sensors. Each temperature
resonator is mounted to its own isothermal block, one having slightly
more mass than the other. As one temperature resonator is given more mass
than the other the sensors will apparently have different time constants.
By mixing the frequency outputs of the two quartz temperature crystal
resonators, the mixer will produce a frequency signal that is
proportional to the temperature difference between the two sensors and
the transducer environment. Amplifying on this, the mixer outputs "bring
forward" a dynamic measurement representing the thermal gradient or
stability of the Quartz Pressure and Temperature Transducer Assembly.
This is the case whether the gradient is induced directly by temperature
change of the environment, or caused by adiabatic effect within the
transducer, due to pressure change. Thus, the dual time-constant
configuration is unique, since it exactly monitors the temperature
response behavior of the transducer embodiment. Together with the
temperature level, the two thermal measurements enhance the fidelity to
correct the gradient disturbance to the pressure and temperature
determination of the transducer.

[0014] According to the present invention, there is provided a transducer
assembly, comprising: four or more crystal controlled oscillators; four
or more thickness shear mode crystal quartz resonators, wherein each
oscillator is controlled by the associated resonator; a first and second
quartz resonator are a pressure and a reference resonator, configured
together as a pressure sensor providing a frequency output; a third
crystal resonator is a temperature resonator, configured as a temperature
sensor providing frequency output; and a fourth crystal resonator is a
temperature sensor. Preferred and optional features of the invention will
be clear from the accompanying claims and from the detailed description
of two illustrative embodiments which follow.

DESCRIPTION OF THE DRAWINGS

[0015] The above description and other features of the present invention
will be more fully understood from the reading of the ensuing description
of the preferred embodiments given with reference to the appended
drawings in which FIGS. 1a, 2a, 3a, . . . etc. refer to a first
embodiment of the present invention, and FIGS. 1b, 2b, 3b, . . . etc.
refer to a second embodiment, in which:

[0016] FIGS. 1a and 1b are schematics showing the outline of the Pressure
and Temperature Transducer Assembly with its main components;

[0017] FIGS. 2a and 2b are another set of schematics representation of the
transducer showing its configuration and signal flow;

[0018] FIGS. 3a and 3b are supplementary schematics to FIGS. 2a and 2b,
respectively, which, in block diagram form only, show the transducer
configuration and the signal routing;

[0019] FIGS. 4a and 4b are schematics showing the primary signal routing
and the pre-processing of the raw resonator sensor signals;

[0020] FIGS. 5a and 5b are schematics showing the full processing of the
pressure determination of the transducer, including the dynamic and
static temperature corrections;

[0021] FIGS. 6a and 6b are schematics showing the full processing chart
for the transducer temperature determination and include the dynamic and
static temperature corrections;

[0022] FIGS. 7a and 7b are schematics of a production well and an
injection well, respectively, showing the heat and heat-flow distribution
due to the process system and earth heat distribution;

[0023] FIGS. 8a and 8b are schematics showing the typical radial heat flow
and the temperature distribution from a producing oil/gas well to the
formation of an application of the invention providing an annular mounted
Pressure and Temperature Transducer Assembly;

[0024] FIGS. 9a and 9b are the same as FIGS. 8a and 8b, except for a
tubular mounted Pressure and Temperature Transducer Assembly; and

[0025] FIGS. 10, 11, and 12 are schematics showing magnified and more
detailed pictures of the 1-dimensional and 2-dimensional radial heat flow
or heat exchange between a warm production fluid and a colder formation;
heat transfer creates isothermal surfaces throughout the wellbore
conduits, and it will be understood that these schematics illustrate the
heat distribution as well as the temperature gradient of a permanent
Pressure and Temperature Transducer Assembly as this invention will see
in an actual mounting location.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Two embodiments of the present invention will be described in
context of pressure and temperature being the primary parameters to be
measured, and to which a transducer 1 is responsive. Figures are included
to show the configuration of the two embodiments of the transducer 1.

[0027] FIG. 1a shows a first embodiment of the present invention. A
section 6 is a thermal block housing the main pressure and temperature
measuring portion of the transducer 1, while a section 7 is the secondary
thermal block housing a gradient temperature sensor 5.

[0028] Two crystals 3 and 4 are shown as being enclosed in the same
environment and protected from pressure by being enclosed in an
atmosphere where the pressure remains constant at all times. They are,
however, subject to the effects of temperature and temperature change.
The temperature change is a function of one or more of the temperature
level, the physical properties of the thermal block 6, and the crystals
2, 3, and 4 as configured, and is characterized by a thermal time
constant 11 (see FIGS. 2a and 3a).

[0029] The crystal 2 is mounted in substantially the same environment as
the crystals 3 and 4, but it is mounted in such a manner that it is
subject to both temperature and pressure. Further, the pressure sensor
crystal 2 is placed in a chamber that is part of and is enclosed by the
thermal block 6, and which is filled with an inert oil-fill. In turn, the
oil-fill is pressurized through a process isolating bellows 15 of which
its exterior is exposed to the environment of the transducer 1. The
temperature gradient crystal sensor 5 is housed in the thermal block 7,
and is enclosed in the same atmosphere as the crystals 3 and 4, which is
being protected from pressure. The temperature gradient sensor 5 is
subject to temperature and temperature change. As with the crystals 3 and
4, the temperature change is a function of temperature level, the
physical properties of the thermal block 7 and the crystal 5 as
configured and characterized by a thermal time constant 12. All of the
crystals referenced are made in thickness shear mode.

[0030] Now, referring to the second embodiment of the invention as shown
in FIG. 1b of the drawings, like reference numerals will be used for the
same features. A section 6 is the thermal block housing the pressure
measuring portion, while a thermal block 7 is the temperature measuring
housing of a transducer 1. The crystals 2 and 3 are shown as being
enclosed in the same thermal block and environment. However, the crystal
3 is protected from pressure by being enclosed in an atmosphere where the
pressure remains constant at all times. They are, however, subject to the
effects of temperature and temperature change as they are part of the
same thermal block 6. The temperature change is a function of the
temperature level, the physical properties of the thermal block 6, and
the crystals 2 and 3 as configured, and is characterized by a thermal
time constant 11 (see FIGS. 2b and 3b).

[0031] The crystal 2 is mounted in substantially the same environment as
the crystals 3 but it is mounted in such a manner that it is subject to
both temperature and pressure. Further, the pressure sensor crystal 2 is
placed in a chamber that is part of and is enclosed by the thermal block
6, and which is filled with an inert oil-fill. In turn, the oil-fill is
pressurized through a process isolating bellows 15 of which its exterior
is exposed to the environment of the transducer 1. Any temperature
gradient or difference within this transducer embodiment 1 is monitored
by the two reference resonators 3 and 5. As the reference resonators 3
and 5 are housed in different thermal blocks 6 and 7, any temperature
change or difference between the two will be detected. As previously
described, the temperature change is a function of the temperature level,
the physical properties of the thermal blocks 6 and 7 as characterized by
a thermal time constants 11 and 12 respectively. As with the crystals of
the first embodiment described above, all of the crystals of this
embodiment are also made in thickness shear mode.

[0032] FIGS. 2a and 2b are supplementary schematic outline drawings of the
two preferred embodiments of the transducer 1, and illustrate more
detailed signals routing from the crystals 2, 3, 4, and 5.

[0033] FIG. 3a is a supplementary schematic to FIG. 2a, and shows the
transducer 1 sensor configuration as an illustrated functional block
diagram of the first embodiment of the present invention. For temperature
measurement, the temperature crystal 4 has a relatively large temperature
coefficient with respect to the reference crystal 3. The temperature
crystal 5 has the same temperature to frequency characteristics as the
temperature crystal 4. The temperature crystal 5 is controlling the
frequency of an oscillator 22. The temperature crystal 4 is controlling
the output of an oscillator 21. The reference crystal 3 is controlling
the frequency output of an oscillator 20. Finally, the pressure crystal 2
is controlling the output of an oscillator 19.

[0034] The outputs 26 and 27 of the oscillators 19 and 20 are fed to a
mixer 23 which produces the difference frequency between the respective
oscillators 19 and 20. A difference frequency 8 is fed into a frequency
counter 16. The output of the frequency counter 16 is in turn fed to a
computer 17 that processes the information from the pressure sensor
signal 8. The output signal 8 from the mixer 23 is called the Pressure
Signal, and is a function of the applied pressure and temperature of the
transducer 1. Furthermore, the output 27 of the oscillator 20 is also fed
directly to the frequency counter 16 and functions as a timebase or a
reference time for the processing of the input frequency signals 8, 9,
and 10.

[0035] In a similar manner, a frequency output 28 of the temperature
oscillator 21 is fed to a mixer 24 and is mixed with the frequency output
27 of the reference oscillator 20. The output difference between the
frequency inputs 27 and 28 produces a beat-frequency or a product 9,
which is input to the frequency counter 16. The mixer output 9 is named
the Temperature Signal, and is a function of the temperature level of the
transducer 1.

[0036] The temperature crystal 5 is controlling the frequency of an
oscillator 22. In turn, the frequency output 29 of the oscillator 22 is
fed to a frequency mixer 25 and is mixed with the frequency output 28 of
the temperature oscillator 21. The mixer 25 produces a frequency output
10 that is named the "Delta Temperature" signal. For the purpose of the
rate and magnitude of the signal 10, the two temperature crystals 4 and 5
have the same temperature sensitivity, but are attached to and are part
of two independent thermal blocks 6 and 7. The thermal blocks 6 and 7 are
configured to have equal or different responses to temperature and
temperature changes over time, which difference is characterized by the
thermal time constants 11 and 12. Changes in temperature of the two
thermal bodies 6 and 7 will change the output of each of the crystals,
and consequently indicate any change and/or difference in temperature
between the two bodies. Thus, the differential temperature between the
bodies 6 and 7 will produce a change in frequency output 10 of the mixer
25, and will be counted and processed by the frequency counter 16 and the
computer 17, respectively.

[0037] In order to prevent ambiguous readings, it is suggested that the
differential temperature measurement is designed so that there are no
convergence points over the range of use. Thus, it is practical to select
the two temperature crystals 4 and 5 so that they have the same
temperature to frequency sensitivity, but have sufficient difference in
nominal frequency so that the frequencies of the two never converge
(become equal) over the temperature and differential temperature range of
use. For example, if the maximum differential temperature expected within
the transducer 1 is 20° C., one would select the nominal frequency
of the temperature crystal 5 so that it converges at a point 25°
C. to 30° C. below the nominal frequency of the temperature
crystal 4.

[0038] Although the temperature crystals 4 and 5 are illustrated as having
a positive temperature coefficient, it is within the scope of this
invention to provide two crystals that have a negative temperature
coefficient, as long as they do not possess ambiguous
frequency-temperature characteristics.

[0039] The crystal resonator 2 is mounted in the same environment 5 as the
crystal resonators 3 and 4 but is separated therefrom. Whereas the
crystal resonators 3 and 4 are housed so as to be free from the effects
of a change in pressure, the crystal resonator 2 is housed inside a
fluid-filled section subject to both temperature and pressure changes.
Furthermore, any changes of temperature within the pressurized system
caused by adiabatic effects will transfer to the thermal block 5 and be
picked up by the temperature resonator 4.

[0040] FIG. 3b is a supplementary schematic to FIG. 2b, and shows the
transducer 1 sensor configuration as an illustrated functional block
diagram of the second embodiment of the present invention.

[0041] For temperature measurement, the temperature crystal 4 has a
relatively large temperature coefficient with respect to the reference
crystal 5 and is controlling the frequency output of an oscillator 21. In
turn, the reference crystal 5 has the same temperature to frequency
characteristics as the reference crystal 3, and is controlling the
frequency output of an oscillator 22. The reference crystal 3 controls
the frequency output of a reference oscillator 20. Finally, the pressure
crystal 2 has a pressure and temperature sensitivity and is controlling
the output of an oscillator 19.

[0042] The outputs 26 and 27 of the oscillators 19 and 20 is fed to a
mixer 23 which produces the difference frequency between the respective
oscillators 19 and 20. A difference frequency 8 is fed into a frequency
counter 16. The output of the frequency counter 16 is in turn fed to a
processor 17 that processes the information from the pressure sensor
signal 8. The output signal 8 from the mixer 23 is called the Pressure
Signal, and is function of the applied pressure and temperature of the
transducer 1. Furthermore, the output 27 of the oscillator 20 is also fed
directly to the frequency counter 16 and functions as a timebase or a
reference time for the processing of the input frequency signals 8, 9,
and 10.

[0043] In a similar manner to the description above, a frequency output 28
of the temperature oscillator 21 is fed to a mixer 24 and is mixed with
the frequency output 29 of the reference oscillator 22. The output
difference between the frequency inputs 28 and 29 produces a
beat-frequency or a product 9, which is input to the frequency counter
16. The mixer output 9 is named the Temperature Signal, and is a function
of the temperature level of the transducer 1.

[0044] The reference crystal 5 is controlling the frequency of an
oscillator 22. In turn, the output of the oscillator 22 is fed to a
frequency mixer 25 and is mixed with the frequency output 27 of the
reference oscillator 20. The mixer 25 produce a frequency output 10 that
is named the "Delta Temperature" or Delta-R signal. For the purpose of
the invention, the two reference crystals 3 and 5 have the same
temperature sensitivity, but are attached and part of two independent
thermal blocks 6 and 7. The thermal blocks 6 and 7 are configured to have
equal or different responses to temperature change, and the difference
between the two is characterized by their thermal time constants 11 and
12. Changes in temperature of the two thermal bodies 6 and 7 will induce
a change in output. Thus, temperature change and a difference in
temperature between the bodies 6 and 7 will produce a change in the
frequency output 10 and will be counted and processed by the frequency
counter 16 and processor 17, respectively.

[0045] In order to prevent ambiguous readings, it is suggested that the
differential temperature measurement is designed so that there are no
convergence points over the range of use. Thus, it is practical to select
the two reference crystals 3 and 5 so that they have the same temperature
to frequency sensitivity, but have sufficient difference in nominal
frequency so that the frequencies of the two never converge (become
equal) over the temperature and differential temperature range of use.
For example, if the maximum differential temperature expected within the
transducer 1 is 20° C., one would select the nominal frequency of
the reference crystal 5 so that it converges at a point 25° C. to
30° C. below the nominal frequency of the reference crystal 3.

[0046] Although the reference crystals 3 and 5 are illustrated as having a
positive temperature coefficient, it is within the scope of this
invention to provide two crystals that have a negative temperature
coefficient cut as long as they do not possess ambiguous
frequency-temperature characteristics.

[0047] The crystal resonator 2 is mounted in the same environment or the
thermal block 6 as the crystal resonator 3. The crystal resonator sets 4
and 5 are separated therefrom, and are placed in their own thermal block
7. However, all crystals are mounted inside the transducer housing 1 and
are exposed to the same temperature environment. Nevertheless, the
crystal resonators 3, 4, and 5 are mounted to be free from the effects of
change in pressure, while, the crystal resonator 2 is housed inside a
fluid filled section of the thermal block 6 and is subject to both
temperature and pressure changes of the transducer 1 environment.
Furthermore, any changes of temperature within the pressurized system
caused by adiabatic effects will transfer to the thermal block 6 and
induce temperature change and difference between the two thermal bodies 6
and 7. In turn, an output change of the frequency output 10 will be
derived by the mixer 25 in response to the gradient condition.

[0048] Now referring to FIG. 4a, the crystal resonator 2 is cut in
thickness shear mode and is both temperature and pressure sensitive. The
crystal resonator 3 is oriented and cut in a manner to be as little
temperature sensitive over the temperature range as possible. However,
the reference resonator 3 possesses some temperature-frequency
characteristics, but these are small compared to those of the crystal
resonators 2, 4, and 5. Hence, when the crystal resonator 2 is subjected
to pressure, there will be an output 8 of the mixer 23 equal to the
difference in frequency between the crystal resonators 2 and 3. The
signal 8, Fp, will be a function of pressure and temperature and the
reference of the transducer. The signal described is called Fp(P,R), and
is input to the frequency counter 16.

[0049] In the same manner, the temperature resonator 4 is part of the same
environment as the crystal resonators 2 and 3, but is made in a cut that
is very sensitive to temperature. By doing so, an outstanding
frequency-temperature response is provided when compared to the
resonators 2 and 3. Hence, when the resonator 4 is subjected to the
temperature, there will be an output 9 FT of mixer 24 that will
equal the difference in frequency between the crystal resonators 3 and 4.
The signal or beat-frequency 9, or FT, will be a function of the
temperature T1 of the thermal block 6 and the reference R of the
transducer 1. The signal and its function is expressed as
FT(T1,R).

[0050] Finally, the crystal resonator 5 is made in the same cut and
sensitivity to temperature as the crystal resonator 4. However, the
crystal resonator 5 is attached to the thermal block 7 and is configured
to a have different time constant to temperature change than the crystal
resonator 4. The crystal resonator 5 is mounted in the same transducer
environment 1 as the crystal resonator 4, but is separated by thermal
response means since the two thermal blocks 6 and 7 are configured to
have different thermal time constants 11 and 12. The crustal resonators 4
and 5 are free from the effects of changes in pressure. However, the
crystal resonator 4 will pick up pressure-induced temperature changes,
e.g., within the thermal block 6, due to adiabatic effects of the
pressure sensing fluid and crystal exposure.

[0051] Upon a temperature change, the two crystal resonators will possess
different thermal response characteristics since the time constant of the
thermal block 6 is different from that of the thermal block 7. The sensor
resonator with the faster thermal response time will "race" or phase-lead
the sensor resonator with the longer thermal response time since there
will be an intermediate or transient period while the temperature
changes, where there will be an apparent temperature difference between
the two during the thermal gradient period. Consequently, as the
resonator output signals 28 and 29 are mixed by the mixer 25, there will
be a change in the output signal every time there is a temperature change
or temperature difference between the two crystal resonators. Moreover,
there will be an output 10 of the mixer 25 that is equal to the
difference in frequency between the crystal resonators, which will be
proportional to the difference in temperature between the two. For
processing means, the output 10 of the mixer 25 is called the "ΔT"
and is expressed as function F(T1,T2). The ΔT signal is a
measure of the thermal stability of the transducer assembly 1. In turn,
the ΔT is used for dynamic correction of the transducer 1 pressure
and temperature determination.

[0052] Now referring to FIG. 4b, the crystal resonator 2 is cut in
thickness shear mode and is both temperature and pressure sensitive. The
crystal resonators 3 and 5 are oriented and cut in a manner to be as
little temperature sensitive over the temperature range as possible.
However, the reference resonators 3 and 5 possess some
temperature-frequency characteristics, but these are small compared to
those of the crystal resonators 2 and 4. Hence, when the crystal
resonator 2 is subjected to pressure, there will be an output 8 of the
mixer 23 that is equal to the difference in frequency between the crystal
resonators 2 and 3. The signal 8, Fp, will be a function of
pressure/temperature and the reference #1 of the transducer. The signal
described is called Fp(P,R.sub.#1), and is input to the frequency counter
16.

[0053] In the same manner, the temperature resonator 4 is part of the same
environment as the reference resonator 5, but is made in a cut that is
very sensitive to temperature. By so doing, the temperature resonator 4
provides an outstanding frequency-temperature response, compared to the
resonators 2, 3, and 5. Hence, when the resonator 4 is subjected to the
temperature, there will be an output 9, named FT, of the mixer 24
that will equal the difference in frequency between the crystal resonator
5 and 4. The signal or beat-frequency 9, will be a function of the
temperature T2 of the thermal block 7. The signal and its function
is expressed as F(T,R.sub.#2).

[0054] Finally, the crystal resonator 5 is made in the same cut and
sensitivity to temperature as the crystal resonator 3. However, the
crystal resonator 5 is attached to the thermal block 7 and is configured
to a have different time constant to temperature change than the crystal
resonator 3. The crystal resonator 5 is mounted in the same transducer 1
environment as the crystal resonator 3, but is separated by thermal
response means since the two thermal blocks 6 and 7, are configured to
have different thermal time constants 11 and 12. the crystal resonators 3
and 5 are free from the effects of changes in pressure. However, the
crystal resonator 3 will pick up pressure-induced temperature changes,
e.g., within the thermal block 6, due to adiabatic effects of the
pressure sensing fluid and crystal exposure.

[0055] Upon temperature change, the two reference crystal resonators will
possess different thermal response characteristics since the time
constant of the thermal block 6 is different from that of thermal block
7. Thus, the reference resonator having the faster thermal response or
time constant, will "race" or phase-lead the sensor resonator with the
with the longer thermal response time. Consequently, there will be an
apparent temperature difference between the two during thermal gradient
periods that induce a change in the output signal 10. The output change
will be equal to the difference in frequency between the reference
crystal resonators 3 and 5, and be proportional to the difference in
temperature (i.e., between the two). For processing means, the output 10
of the mixer 25 is called the ΔR and is expressed as function
F(R.sub.#1,R.sub.#2). The ΔR signal is a measure of the thermal
stability of the transducer assembly 1. In turn, the ΔR is used for
dynamic correction of the transducer 1 pressure and temperature
determination.

[0056] FIGS. 5a and 5b are the signal processing charts for the pressure
determination of the two illustrated embodiments of the transducer 1.
Outputs of the mixers 23, 24, and 25 are all fed into a Dynamic Block 13
that produces a corrective signal "e" to the output 8 of the crystal
resonator 2. Within the dynamic block 13, the pressure mixer output 8 is
mixed with the corrective frequency output "e" of the dynamic temperature
correction model. The dynamic block 13 is made so that it processes no
corrective output "e" at static temperature conditions. By these means,
the nature of the dynamic block 13 is such that it provides no corrective
effect to the transducer 1 pressure determination when the temperature of
the transducer 1 is in steady state and there is no difference in
temperature between the two internal thermal bodies 6 and 7.

[0057] Correspondingly, if there is a temperature change or difference in
temperature between the thermal bodies 6 and 7, the dynamics of the block
13 will produce an output "e," equal to the anticipated frequency offset
of the crystal resonator 2 caused by the temperature change or
difference. By dynamics means, the corrected signal 30 is a multivariate
function of which diffusivity coefficients are biased by the pressure and
temperature levels 8 and 9, and is proportional to the temperature change
or difference monitored by the output 10. The thermally corrected signal
30 is named FP' and fed to the Static Block 32 for traditional
temperature correction and linearization means. For those skilled in the
art, it should be recognized that to achieve the optimum accuracy of the
transducer 1 pressure determination it might be preferable to make sets
of different values for the dynamic and static coefficients dedicated to
each transducer manufactured. In turn, the coefficients that are derived
typically depend on what temperature and pressure ranges are expected to
be encountered. Both corrections and models, i.e., the dynamic block 13
and the static block 32, are not physical hardware functions, but are
implemented in software, and are included as signal processing tasks of
the processor 17. However, they are both thermal correction models which
account for the thermal dynamics of the transducer 1 crystal resonators.

[0058] FIGS. 6a and 6b are the signal processing charts for the
temperature determinations of the two illustrated embodiments of the
transducer 1. Outputs of the mixer 24 and 25 are all fed into a Dynamic
Block 14 that produces a corrective signal "e" to the output 9 of the
crystal resonator 4. Within the dynamic block 14, the temperature mixer
output 9 is mixed with the corrective frequency output "e" of the dynamic
temperature correction model. The difference in frequency between the two
equals the output signal 31, which in turn is thermally corrected. As
with the dynamic correction block 13, the nature of the dynamic block 14
is such that it provides no corrective effect on the transducer 1
temperature determination, since the temperature of the transducer 1 is
at steady state and there is no difference in temperature between the two
thermal bodies 6 and 7.

[0059] Conversely, if there is a temperature change or difference in
temperature between the thermal bodies, the dynamics of the block 14 will
produce an output "e," equal to the anticipated frequency offset of the
crystal resonator 4 caused by the temperature change or difference in
progress. The corrected temperature signal 31 is a multivariate function,
and its diffusivity coefficients are biased by the temperature level 9.
In turn, the block output is proportional to the temperature difference
and is a function of output 10. The thermally corrected signal 31 is
named FT', and is fed to the Static Block 33 for traditional
linearization means.

[0060] For those skilled in the art, it should be recognized that to
achieve the optimum accuracy of the transducer 1 temperature
determination it might be preferable to make sets of different values for
the dynamic and static coefficients that are dedicated for each
transducer manufactured, and are depending upon what temperature ranges
are expected to be encountered. Both correction models, i.e., the dynamic
block 14 and the static block 33, are not physical hardware functions but
are implemented in software, and are included as a signal processing
tasks of the processor 17. However, they are both thermal correction
models, which accounts for the thermal dynamics of the transducer 1
crystal resonators.

[0061] For the purpose of the invention, FIGS. 7a and 7b illustrate
different service type wells. FIG. 7a shows a production type well, and
FIG. 7b shows an injection type well. Both wells' production tubing is
used to transport a process media consisting of gas, fluid, or a
combination of both. In both applications illustrated, the process media
contribute to heat transfer by convection and conduction. As within any
thermal application, heat is transferred from a hot environment to a cold
environment. Thus, heat will flow and transfer in the two applications as
illustrated, creating a two-dimensional (axial and radial) cross
sectional temperature profile.

[0062] FIGS. 8a, 8b, 9a, and 9b show in greater detail the transducer 1
location as mounted to the well completion. In FIGS. 8a and 8b, the
transducer 1 is attached to the wall of the wellbore casing, and in FIGS.
9a and 9b, it is attached to the tubing or completion. FIGS. 8 and 9 show
the well in cross-sectional views, and illustrate the radii temperature
profile as induced by heat transfer.

[0063] Referring to FIGS. 10, 11, and 12, these figures show a more
detailed view of the wellbore temperature profile in respect to the
transducer 1 and its mounting. FIG. 10 shows the envisioned temperature
profile induced by heat conduction from the production media through the
wellbore conduits. FIG. 11 shows the one-dimensional heat conduction in a
well with a permanent pressure and temperature transducer installed. FIG.
12 shows the heat flow in the quartz pressure and temperature transducer,
with an assumption that temperature t3 is greater than temperature
t4.

[0064] The figures are made for the purpose of this invention to
illustrate the need for dynamic temperature correction means since the
transducer 1 mounting location is by definition inside a thermal gradient
zone. Moreover, due to process load changes, the illustrated temperature
profile will fluctuate and induce thermal gradients within the transducer
1. The temperature profile within the transducer 1 is illustrated by the
lines of heat-flow 36 and isothermals 37 (see FIG. 12) in the direction
of heat drop or transfer through the transducer cross-section. Due to
heat transfer from the well to the surrounding formation, the transducer
1 is held at high t3 (38) at one side and low t4 (39) where the
heat exit. Again, this is to illustrate the need for dynamic temperature
correction of the transducer 1 pressure and temperature determination as
required by gradient environment and location.

[0065] Although the foregoing description of the present invention has
been shown and described with reference to particular embodiments and
applications thereof, it has been presented for purposes of illustration
and description and is not intended to be exhaustive or to limit the
invention to the particular embodiments and applications disclosed. It
will be apparent to those having ordinary skill in the art that a number
of changes, modifications, variations, or alterations to the invention as
described herein may be made, none of which depart from the spirit or
scope of the present invention. The particular embodiments and
applications were chosen and described to provide the best illustration
of the principles of the invention and its practical application to
thereby enable one of ordinary skill in the art to utilize the invention
in various embodiments and with various modifications as are suited to
the particular use contemplated. All such changes, modifications,
variations, and alterations should therefore be seen as being within the
scope of the present invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are fairly,
legally, and equitably entitled.